bug#43773: guix offload scheduler/load balancer throttles itself

[Maxim Cournoyer]

Hello,

Guix offload monitors the load of the offload machine, and waits
patiently until the load comes back down below a pre-determined level
(normalized 2.0 level, it seems) before starting the next build, even
when there is a single offload build machine involved.  This is
inefficient and causes it to throttle itself.

Idea of an improvement: it should choose the offload machine with the
less load (already the case, I believe), and not block waiting for the
load to go down before starting a build.

Maxim